Modem implantable cardiac generators such as cardioverters, defibrillators or pacers supply an electrical therapy to the heart. Many implantable cardioverter defibrillators deliver a tired therapy for the treatment of tachyarrhythmia and biphasic pulses for the treatment of fibrillation. That is the device operates in a conventional pacing modality for brady arrhythmia providing micro Joules of energy. Tachy arrhythmia may be treated automatically by the delivery of synchronized low energy pulses, while bouts of fibrillation may be treated with several Joules of energy. Given the wide range of energies delivered it has been difficult to design lead systems offering good performance for each of these therapies and there is a continuing need to improve lead design.